Transistor ignition system



May 24, 1966 s. ROBBINS 3,253,168

TRANSI STOR IGNITION SYSTEM Original Filed Aug. 6, 1962 INVENTOR. 5A M (/E L 5. ROBE/N5 BY lg m A TTORNE) United States Patent 3,253,168 TRANSISTOR IGNITION SYSTEM Samuel B. Robbins, Rochester, Mich., assignor to General Motors Corporation, Detroit, Mich, a corporation of Delaware Original application Aug. 6, 1962, Ser. No. 215,081. Divided and, this application Aug. 10, 1964, Ser. No.

3 Claims. (Cl. 310-70) This invention relates to an ignition system for internal combustion engines and more particularto an ignition system wherein a semiconductor such as a transistor controls the current flow in the primary winding of the ignition coil. This application is a division of application S.N. 215,081, filed on August 6, 1962.

One of the problems encountered in the use of transistor ignition systems is the destructive kick back voltage which comes from the primary Winding when the current flow to the primary winding is interrupted and which under certain conditions can destroy the transistor that controls primary current. In some instances, diodes and combinations of diodes and resistors have been used to block the kick back voltage or to provide a current path around the transistor for the energy developed by the kick back voltage.

One of the objects of this invention is to provide an ignition system wherein the kick back voltage is used to build up energy for firing a spark plug. This object is accomplished by continuously reversing the current flow through the primary winding of the ignition coil so that when an inverse kick back voltage occurs, the current flowing through the primary winding from 'a DC. source is in the same direction as the current developed by the kick back voltage. In this system, transistors are used to control the current'flow through the primary winding and the transistors are connected to provide current flows for the primary winding that are alternating in opposite directions.

Still another object of this invention is to provide a completely'breakerless ignition system which is capable of causing a reversal incurrent through the primary winding of an ignition coil during operation of the ignition system.

A more specific object of this invention is to provide a transistor ignition system wherein the conduction of the transistors is controlled by a magnetic pick up device which has a center tapped pick up coil and a rotor which rotates relative to the pick up coil and which has sectors of alternate opposite magnetic polarities.

Another object of this invention is to provide a volt age pulse generating device which can be used to control a semiconductor ignition system or the like and which has-an A.C. output that is substantially a square wave. This type of output voltage is useful since it can instantaneously reverse the bias voltage applied to one or more semiconductors such as transistors to cause them to switch sharply from one condition'to the other. This object is carried forward'by providing a magnetic rotor which has radially extending pole teeth that cooperate with the pole faces of a core. The rotor pole teeth have the .same width and are spaced from each other by this same width. In addition, the pole faces of the core are spaced this same width and the pole faces themselves have the same width. As' a result of this, the voltage output is an alternating square wave which is capable of sharply switching semiconductors such as transistors.

Further objects and advantages of the present invention will be apparent from the following description,

reference being had to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

- engine.

In the drawings:

FIGURE 1 is a schematic circuit diagram of an ignition system made in accordance with this invention.

FIGURE 2 is a top view of a magnetic pick up device for controlling the ignition system of FIGURE 1.

FIGURE 3 is a side view of the magnetic pick up device illustrated in FIGURE 2.

Referring now to the drawings and more particularly to FIGURE 1, the reference numeral 10 designates an internal combustion engine which has a plurality of spark plugs 12 for firing the combustible mixture of the In this particular instance, there are eight spark plugs for an eight cylinder engine but it will be apparent to those skilled in the art that the number of spark plugs can vary with the number of cylinders in the engine. The spark plugs 12 are connected with the electrodes 14 on a conventional distributor cap generally designated by reference numeral 16. A rotor member 18 is driven in synchronism with the engine and is driven in synchronism with a rotor member 20 of a magnetic pick up which is more fully described hereinafter. The rotor contact 18 is electrically connected with a lead wire 22 coming from the secondary winding 24 of an ignition coil 26.

It is seen that the opposite side of the secondary winding 24 is grounded and that theignition transformer 26 has a primary winding 28. g

The current flow through the primary winding 28 is controlled by a plurality of semiconductor devices which in this case take the form of PNP transistors 30, 32, 34 and 36 It can be seen that the emitter electrodes of transistors 30 and 34 are connected with a lead wire The base electrode of transistor 30 is connected with a junction 40 while the base electrode of transistor 34 is connected with junction 42. The collector electrode of transistor 30 is connected with junction 44 and it can be seen that this junction is connected to one side of the primary winding 28 by a conductor 46. The

collector electrode of transistor 34 is connected with base electrode of transistor 36 is connected with junction' 60 via the lead wire 58.

Ignition'power forthe ignition system is supplied by a DC. voltage source 64 which is illustrated as a battery. It will of course be appreciated that the battery supplies ignition power during cranking of the engine but that ignition power thereafter is supplied by a generator which also charges the battery in a motor vehicle system. In any event, ignition power is supplied to the system either from the battery or from a generator through a conductor 66 and a manually operable ignition switch 68.

A resistor 70 connects the junction 40 with conductor 66 and another resistor 72 connects the conductor 56 with junction 54. A resistor 74 is connected between lead wires 66 and 38.

The conduction of transistors 30 through 36 is transistors 76 and 78. The emitter electrode of transistor 76 is connected with junction 60 while the collector electrode ofthis transistor is connected with grounded junction 80. The base electrode of transistor76'is connected with junction 82.

The emitter electrode of transistor 78 'is connected with junction 42 while the collector electrode of this tran.

Patented May 24, 1966 controlled by a magnetic pick-up device and a pair of PNP.

sistor is grounded at junction 80. The base electrode of transistor 78 is connected with junction 84.

A resistor 86 cnnects the junctions 82 and 88 and another resistor 90 connects the junctions 88 and 84. It is seen that junction 88 is connected with junction 92 on the powersupply conductor 66.

The magnetic pick up assembly for controlling the ignition system is illustrated in FIGURES 2 and 3. This magnetic pick up assembly includes a base 94 which rotatably supports a shaft 96 that is driven by the engine. The shaft 96 carries the rotor which is formed of a nickel material and which has eight radially directed pole tips or arms which are magnetized with opposite polarities as is depicted in FIGURE 2. In other words, the arm or pole tip 100 has a south polarity whereas the arm or pole tip 102 has a north polarity. This sequence continues for the other six pole tips as is clear from an inspection of FIGURE 2. The nickel rotor is permanently magnetized by a suitable magnetizing fixture so that the pole tips are permanently magnetized in a manner illustrated in FIGURE 2. The rotor thus is a permanent magnet with the pole tips having alternate opposite magnetic polarities. The arcuate ends of the pole tips are the same circumferential length as the gaps between the pole tips. In the embodiment illustrated, each arcuate end of a pole tip and gap is one sixteenth of a circle for an eight cylinder engine but this of course would change to one twelfth for a six cylinder engine, one eighth for a four cylinder engine and so forth.

The pick up coil assembly is generally designated by reference numeral 104 and is supported on a timing plate 106 which can be adjusted relative to the base 94. This timing plate can be shifted around the axis of the shaft 96 by a suitable vacuum unit which is not illustrated and which would be connected with the intake manifold of the engine 10. The magnetic pick up assembly includes a laminated core 108 formed of magnetic material such as steel laminations. A coil winding 110 is wound on the core and this coil winding is center tapped at 112 as is apparent from FIGURE 1. This center tap is grounded by lead wire 114 illustrated in FIGURE 1 and in FIG URE 2. It is seen that the ends 108a and 108b of the core 108 are arcuately shaped.

The pole faces 108a and 1081; have the same arcuate length as the pole tips of rotor 20 and the gap between these pole faces is the same arcuate length of the pole faces 108a and 108b.

It will be appreciated that as the rotor 20 rotates, the flux passes from one pole tip then through the magnetic core and then back to another pole tip. Thus with the rotor in the position shown in FIGURE 2, the flux can flow from pole tip 102, through the magnetic core 108 and then back to the pole tip 103. This, of course, will cause a voltage to be induced in the center tapped coil winding 110. It can be seen that as the rotor rotates, the magnetic flux is continuously reversed in the magnetic core 108. In other words, the pole tip 102 is a north pole but when the rotor rotates so that pole tip 100 aligns with core face 108a, the flux through the core 108 is reversed in direction from the direction of flux flow with the parts in the position illustrated in FIGURE 2. It will be appreciated that there are only short instants of time wherein during movement of the rotor with respect to the core when the rotor pole tips are not aligned with at least some port of the pole faces 108a and 108b. During these instants, the field collapses and is instantly built up in the opposite direction. This provides a square wave voltage output which can sharply switch the transistors in a manner to be more fully described.

The operation of the ignition system of this invention will now be described. When ignition switch 68 is closed, the power line 66 is connected with one side of the direct current power source 64. This biases the transistors 76 and 78 .to their nonconductive states since a positive voltage is applied to their base electrodes through junction 92 and resistors 86 and 88. It can be seen that the base current path for transistors 30 and 36 is through the emitter-collector circuit of transistor 76 and since this transistor is now off, the transistors 30 and 36 are turned off in their emitter-controller circuits. The base current path for transistors 32 and 34 is through the emitter-collector circuit of transistor 78 and since this transistor is likewise turned off, the transistors 32 and 34 are turned off.

As the rotor 20 rotates, the voltage induced in the pick up coil will at certain positions of rotor 20 have a polarity as indicated in FIGURE 1 but this polarity will then be sharply reversed during continued rotation. This polarity thus continuously sharply reverses as the rotor 20 rotates.

When the voltage induced in the coil winding has the polarity shown in FIGURE 1, the base of transistor 76 is driven positive whereas the base of transistor 78 is driven negative, With the base of transistor 78 negative, a base current flows in transistor 78 to turn it on in its emitter-collector circuit. This completes a base current path for transistors 32 and 34 and they turn on intheir emitter-collector circuits.

traced for supplying current to the primary winding 28' A circuit may now be which is from junction 92, through lead wire 66, through resistor 74, through lead wire 38, through the emittercollector circuit of transistor 34, throughthe primary winding 28 through lead wire 46, through the emittercollector circuit of transistor 32 and then to ground via junction 52. This will cause a build up of current in the primary winding 28 with current flowing through this winding in the direction of the arrow indicated in FIGURE 1.

core 108, the voltage induced in the coil winding 110 is sharply reversed from its polarity shown in FIGURE 1. This drives the base electrode of transistor 78 positive to turn it off and therefore turn off transistors 32 and 34. At the same time, the base electrode of transistor 76 is driven negative so it now conducts. transistor 76 conducting, there is a base current path for transistors 30 and 36 and a circuit can now be traced in a reverse direction through primary winding 28. This circuit is from lead wire 66, through resistor 74, through lead wire 38, through the emitter-collector circuit of transistor 30, through lead wire 46, through primary winding 28, and then through the emitter-collector circuit of transistor 36 to ground. It can be seen from the foregoing that as the rotor rotates, a pair of transistors shut off, for example, transistors 32 and 34, while the other pair of transistors 30 and 36 turn on. effect of this is to break the circuit to the primary Winding 28 for one direction of current flow which previously has been building up and then to complete a circuit for the primary winding for current flow in an opposite direction. During reversal of current flow through the primary winding 28, a high voltage is induced in the secondary winding 24 which causes one of the spark plugs 12 of fire. The kick back voltage of primary winding 28 will be in the same direction as the next built up of current since the circuit for the primary winding is interrupted for one direction of flow but is then completed for another direction of current flow.

The resistors 86 and 88 are bias resistors for the base electrodes of transistors 76 and 78 as are the resistors 70 and 72 for the transistors 30 through 36. The resistor 74 is a current limiting resistor.

The particular construction of the magnetic pick up of this invention plays an important part in insuring correct operation of the system. Thus, by using a magnetic switching action is attained with a square wave voltage output.

With

The net i While the embodiments of the present invention as herein disclosed, constitute a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. A pulse generator for controlling a semiconductor ignition system comprising, a base, a shaft supported by said base and adapted to be driven by an engine, a rotor driven by said shaft having a plurality of radially extending and circumferentially spaced arms, said rotor being a permanent magnet with its arms having alternate opposite magnetic polarities, a timing plate, and a coil assembly supported by said timing plate including a core member formed of magnetic material and a coil winding wound on said core member, said coil winding being tapped intermediate its ends, the ends of said arms cooperating with the pole faces of said core member and having equal lengths which are substantially equal to the gaps between the arms.

2. A voltage pulse generator for triggering a semiconductor ignition system comprising, a base member, a shaft rotatably supported by said base member and adapted to be driven by an engine, a permanent magnet rotor driven by said shaft having a plurality of radially extending and circumferentially spaced arms magnetized with alternate opposite magnetic polarities, a timing plate adjustable relative to said rotor, a coil assembly supported by said timing plate including a magnetic core carrying a coil winding, said magnetic core having pole faces cooperating with the pole faces of said arms, the lengths of said pole faces of said arms, the length of the gap between said arms, the length of the gap between the pole faces of said core member and the length of the pole faces of said core member all being substantially equal.

3. The pulse generator according to claim 2 where the coil winding that is wound on the core member is tapped intermediate its ends.

References Cited by the Examiner UNITED STATES PATENTS 2,071,573 2/1937 Randolph et a1. 310-156 2,089,759 8/1937 Nowosielski 310156 2,131,523 9/1938 Quintavalle 310-l56 2,612,887 10/1952 MacKay 310- ORIS L. RADER, Primary Examiner.

A. I. ROSSI, Assistant Examiner. 

1. A PULSE GENERATOR FOR CONTROLLING A SEMICONDUCTOR IGNITION SYSTEM COMPRISING, A BASE, A SHAFT SUPPORTED BY SAID BASE AND ADAPTED TO BE DRIVEN BY AN ENGINE, A ROTOR DRIVEN BY SAID SHAFT HAVING A PLURALITY OF RADIALLY EXTENDING AND CIRCUMFERENTIALLY SPACED ARMS, SAID ROTOR BEING A PERMANENT MAGNET WITH ITS ARMS HAVING ALTERNATE OPPOSITE MAGNETIC POLARITIES, A TIMING PLATE, AND A COIL ASSEMBLY SUPPORTED BY SAID TIMING PLATE INCLUDING A CORE MEMBER FORMED OF MAGNETIC MATERIAL AND A COIL WINDING WOUND ON SAID CORE MEMBER, SAID COIL WINDING BEING TAPPED INTERMEDIATE ITS ENDS, THE ENDS OF SAID ARMS COOPERATING WITH THE POLE FACES OF SAID CORE MEMBER AND HAVING EQUAL LENGTHS WHICH ARE SUBSTANTIALLY EQUAL TO THE GAPS BETWEEN THE ARMS. 